I found a small plumbing shop open late and bought 4 meters of 1/2in copper tubing and made a loop this evening. I had no high voltage capacitors so cut various lengths of RG-58A to use as coax caps and kluged a Faraday shielded loop coupling system to drive the main loop. None of it is permanent yet but after only working on it for 30 minutes total, I have been amazed how well it works with the low power version K2. … The bandwidth for 2:1 SWR on 20 is 80khz without retuning the center of which is 1:1.

The loop radius is 4/pi/2m, conductor radius is 0.064m, frequency is 14MHz, and VSWR=2 bandwidth is 80kHz.

Above is the calculator result, estimated efficiency is just 8.5%, quite low for a loop of this diameter on 20m so there is lots of room for improvement.